1. Field of the Invention
The present invention relates to a PWM control device for PWM controlling an output current of an inverter circuit, and a motor-driven blower and an electric vacuum cleaner each equipped with an electric motor driven by the output current thereof PWM-controlled by the PWM control device. The electric vacuum cleaner described herein includes various devices, which collect various solids or fluids to a collection region through the use of negative pressure.
2. Description of the Related Art
As a conventional motor-driven blower, there has been known one having an overcurrent protecting function which determines an inrush current (overshoot current) and an unusual or improper current at its startup. In this type of motor-driven blower, a current I that flows through a brushless motor of the motor-driven blower, increases instantaneously but decreases with time upon the startup of the motor-driven blower as shown in FIG. 12. On the other hand, when the brushless motor is overloaded continuously or the motor-driven blower is brought into a locked state, an excessive current continues to flow.
Therefore, an overcurrent detected value Iz and an overcurrent detected time Tz are set and detected simultaneously. By doing so, the inrush current at the startup and the improper current can be discriminated or determined. Namely, if Tz less than Tb is taken when Iz less than I, then the improper current is found to have occurred and the current is interrupted. Various circuit configurations each having such a function has heretofore been proposed.
According to such means, however, a large current will flow upon the startup of the motor-driven blower while the time is exactly short, thus applying a load to each of electronic parts on an electric circuit. Therefore, there has been proposed a technology, which suppresses the inrush current at the startup as much as possible. There is known, for example, a method disclosed in Unexamined Patent Publication No. Sho 62(1987)-272877, wherein a signal having a short pulse width is outputted in a PWM inverter device only for a predetermined time upon the startup of the motor-driven blower to start up the motor-driven blower.
However, Unexamined Patent Publication No. Sho 62(1987)-272877 does not disclose any specific means for outputting the signal having the short pulse width upon the startup of the motor-driven blower.
An object of the present invention is to provide means easy to be implemented as means for PWM-controlling a current to be supplied to an electric motor so as to decrease upon startup of the electric motor, and provide means which reduces an inrush current (overshoot current) at the startup of the electric motor, particularly reduces an on-startup inrush current, which is suitable for an application like a motor-driven blower.
The object of the present invention is achieved by the novel PWM control device, motor-driven blower and electric vacuum cleaner of the present invention.
The present invention provides a PWM control device wherein a microprocessor determines a pulse width of a PWM signal through the use of a signal detected by rotation position detecting means which detects the rotational position of a rotor of a brushless motor, with respect to the amount of each current supplied from an inverter circuit for driving the brushless motor to the brushless motor to thereby perform PWM control. Under the PWM control, the microprocessor enlarges the pulse width of the PWM signal during an interrupt processing or process including a process for detecting the rotational position by the rotation position detecting means upon startup of the brushless motor and gradually enlarges the pulse width of the PWM signal according to the repetition of the interrupt processing, thereby making it possible to easily limit or suppress an inrush or overshoot current with respect to each current supplied to the motor upon startup of the motor.
The present invention according to another aspect provides a motor-driven blower which includes a brushless motor, an air blower rotatably driven by the brushless motor, an inverter circuit which drives the brushless motor, rotation position detecting means which detects a rotational position of rotor of the brushless motor, and a PWM control device wherein a microprocessor determines a pulse width of a PWM signal through the use of a signal detected by the rotation position detecting means, with respect to the amount of each current supplied from the inverter circuit to the brushless motor to thereby perform PWM control. Under the PWM control, the microprocessor enlarges the pulse width of the PWM signal during interrupt processing including a process for detecting the rotational position by the rotation position detecting means upon startup of the brushless motor and gradually enlarges the pulse width of the PWM signal according to the repetition of the interrupt processing, thereby making it possible to easily limit or suppress an inrush or overshoot current with respect to each current supplied to the motor upon startup of the motor.
The present invention according to a further aspect provides a cleaner comprising a brushless motor, an air blower rotatably driven by the brushless motor, an inverter circuit which drives the brushless motor, rotation position detecting means which detects a rotational position of rotor of the brushless motor, and a PWM control device wherein a microprocessor determines a pulse width of a PWM signal through the use of a signal detected by the rotation position detecting means, with respect to the amount of each current supplied from the inverter circuit to the brushless motor to thereby perform PWM control. Under the PWM control, the microprocessor enlarges the pulse width of the PWM signal during interrupt processing including a process for detecting the rotational position by the rotation position detecting means upon startup of the brushless motor and gradually enlarges the pulse width of the PWM signal according to the repetition of the interrupt processing, thereby making it possible to easily limit or suppress an inrush or overshoot current with respect to each current supplied to the motor upon startup of the motor.